Biology subjects

Ryglewski, S.

Publications and source records attributed to Ryglewski, S..

5 recordsLinked to original sources

bioRxiv2025

Robustness through variability: ion channel isoform diversity safeguards neuronal excitability

Neural circuits are composed of different neuron types that exhibit distinctly different computational properties resulting from the sets of ion channels expressed. Profound insight exists into how neural computations arise from the precise regulation of ion channels (Armstrong et al., 1998; Lai, Jan, 2006; Nusser et al., 2012), how degenerate channel properties support similar computations (Marder, Prinz, 2002; Marder, Goaillard, 2006), and how channelopathies affect brain function (Kullmann, 2010). However, it remains elusive why neurons express many more channels, and isoforms thereof, than required to tune their specific excitabilities. Here, we employ an experiment-theory approach pairing electrophysiology with Drosophila genetics, and mathematical modelling to show that the variance in membrane properties that results from ion channel diversity promotes the robustness of neuron-type specific functions. Specifically, we show that the robustness of flight motoneuron coding properties to internal and external perturbations is significantly enhanced by the diversity of calcium channel splice isoforms expressed. Importantly, increased excitability robustness to perturbations of outward currents or temperature does not require adjustments in calcium channel mean properties. Instead, increases of the variance of calcium channel gating properties that result from channel isoform diversity broaden the dynamic input range the neuron can compute without reaching depolarization block. This broadens our concept of the functional consequences of the tremendous variety and diversity of ion channels expressed in brains. One Sentence SummaryThe variance of calcium channel gating properties is increased by channel isoform diversity and aids neuronal coding and excitability robustness.

neuroscience↗

bioRxiv2025

Motoneurons can count: A cell intrinsic spike number memory compensates for deviations from rate coding

Firing rate is an important means of encoding information in many types of neurons. A prime example is asynchronous flight as used by [~]600,000 insect species (Dudley, 2018), where wingbeat frequency and flight power output are controlled by a rate code of the flight power motoneurons (Hurkey et al., 2023). The five motoneurons that innervate the wing depressor muscle fibers translate different magnitudes of excitatory drive smoothly into changes of their common firing rates, which in turn, are linearly related to wing power output (Gordon and Dickinson, 2006). Such motoneuron input/output properties are called type-I excitability and are achieved by the expression of specific combinations of ion currents that linearize the frequency-input current curve. But are there additional motoneuron properties that compensate for acute perturbation of their rate code? Here we combine in vivo electrophysiology with Drosophila genetics to test for mechanisms that compensate for transient perturbation of rate coding during behavior. We show that MN intrinsic properties compensate for the occurrence of extra spikes by delaying the subsequent spikes, thus restoring rate coding fidelity. The underlying mechanism is dose and phase dependent. First, compensatory increases of subsequent interspike interval durations grow with the number of supernumerous spikes that interfere with coding. Second, the magnitude of the compensation for single extra spikes depends on when during an interspike interval these occur. This mechanism depends at least in part on axonally localized HCN channels and increases the fidelity of motoneuron rate coding in the light of perturbation during flight motor behavior.

neuroscience↗

bioRxiv2024

Specific presynaptic functions require distinct Drosophila Cav2 splice isoforms

The multiplicity of neural circuits that accommodate the sheer infinite number of computations conducted by brains requires diverse synapse and neuron types. At many vertebrate synapses release probability and other aspects of presynaptic function are tuned by different combinations of Cav2.1, Cav2.2, and Cav2.3 channels. By contrast, most invertebrate genomes contain only one Cav2 gene. The one Drosophila Cav2 homolog, cacophony (cac), localizes to presynaptic active zones (AZs) to induce synaptic vesicle release. We hypothesize that Drosophila cac functional diversity is enhanced by two specific exon pairs that are mutually exclusively spliced and not conserved in vertebrates, one in the voltage sensor and one in the intracellular loop containing the binding site(s) for Ca{beta} and G-protein {beta}{gamma} subunits. We test our hypothesis by combining opto- and electrophysiological with neuroanatomical approaches at a fast glutamatergic model synapse, the Drosophila larval neuromuscular junction. We find that alternative splicing in the voltage sensor affects channel activation voltage and is imperative for normal synapse function. Only the isoform with the higher activation voltage localizes to the presynaptic AZ and mediates evoked release. Removal of these cac splice isoforms renders fast glutamatergic synapses non-functional. By contrast, alternative splicing at the other alternative exon that encodes the intracellular loop between the first and the second homologous repeats does not affect cac presynaptic AZ localization, but it tunes multiple aspects of presynaptic function. While expression of one exon yields normal transmission, expression of the other exon reduces channel number in the AZ and thus release probability. This also abolishes presynaptic homeostatic plasticity. Moreover, reduced channel number upon selective exon excision increases paired pulse ratios and the variability of synaptic depression during low frequency stimulation trains (1 and 10 Hz), and thus affects short term plasticity. Effects on short term plasticity can be rescued by increasing the external calcium concentration to match release probability to control. In sum, in Drosophila alternative splicing provides a mechanism to regulate different aspects of presynaptic functions with only one Cav2 gene.

neuroscience↗

bioRxiv2022

Insect asynchronous flight requires neural circuit de-synchronization by electrical synapses

Despite profound mechanistic insight into motor pattern generation, for asynchronous insect flight - the most prevalent form of flight employed by >600.000 species - architecture and function of the underlying central pattern generating (CPG) neural network remain elusive. Combining electro- and optophysiology, Drosophila genetics, and mathematical modelling, we uncover a miniaturized circuit solution of motoneurons interconnected by electrical synapses that, contrary to doctrine, serve to de-synchronize network activity. This minimal gap-junctional motoneuron network suffices to translate unpatterned premotor input into stereotyped firing sequences which are conserved across species and generate stable wingbeat power. Mechanistically, network de-synchronization requires weak electrical coupling in conjunction with specific postsynaptic excitability dynamics, revealing an unexpected, generic feature in the control of neural circuit dynamics by electrical synapses. One Sentence SummaryElectrical synapses de-synchronize neural network firing to enable stable wingbeat power during insect flight.

neuroscience↗

bioRxiv2019

Different α2δ Accessory Subunits Regulate Distinctly Different Aspects of Calcium Channel Function in the Same Drosophila Neurons

Voltage gated calcium channels (VGCCs) regulate neuronal excitability and translate activity into calcium dependent intracellular signaling. The pore forming 1 subunit of high voltage activated (HVA) VGCCs operates not in isolation but associates with 2{delta} accessory subunits. 2{delta} subunits can affect calcium channel biophysical properties, surfacing, localization and transport, but their in vivo functions are incompletely understood. In vertebrates, it is largely unknown whether different combinations of the four 2{delta} and the 7 1 subunits mediate different or partially redundant functions or whether different 1/2{delta} combinations regulate different aspects of VGCC function. This study capitalizes on the relatively simpler situation in the Drosophila genetic model that contains only two genes for HVA calcium channels, one Cav1 homolog and one Cav2 homolog, both with well-described functions in different compartments of identified motoneurons. We find that both d2{delta}1 and d2{delta}3 (stj) are broadly but differently expressed in the nervous system. Both are expressed in motoneurons, but with differential subcellular localization. Functional analysis reveals that d2{delta}3 is required for normal Cav1 and Cav2 current amplitudes and for correct Cav2 channel function in all neuronal compartments, axon terminal, axon, and somatodendritic domain. By contrast, d2{delta}1 does not affect Cav1 or Cav2 current amplitudes or presynaptic function, but it is required for correct Cav2 channel allocation to the axonal versus the dendritic domain. Therefore, different 2{delta} subunits are required in the same neurons to precisely regulate distinctly different functions of HVA calcium channels, which is in accord with specific 2{delta} mutations causing different brain diseases.\n\nSignificance StatementCalcium influx through the pore forming 1-subunit of voltage gated calcium channels serves essential neuronal functions, such as synaptic vesicle release, control of action potential shape and frequencies, synaptic input computations, and transcriptional control. Localization and function of 1-calcium channel subunits depend on interactions with 2{delta} accessory subunits. Here we present in vivo analysis of Drosophila motoneurons revealing that different 2{delta} subunits independently regulate distinctly different aspects of calcium channel function in the same neuron, such as current amplitude and dendritic versus axonal channel localization. Our findings start unraveling how different 1/2{delta} combinations regulate functional calcium channel diversity in different sub-neuronal compartments, and may provide an entry point toward understanding how mutations of different 2{delta} genes underlie brain diseases.

neuroscience↗